The present invention is directed towards a ground fault interruptor circuit and, more particularly, a ground fault interruptor circuit utilizing an electronic latching circuit
Ground fault interruptor circuits interrupt the application of electric power to a load in response to an imbalance of a predetermined magnitude in the current flowing through the current-carrying wires connected between the source and the load. Typically, a ground fault interruptor circuit will use one or more differential transformers to monitor the current through the hot and neutral lines extending between a load and a source of power and will generate a fault signal whenever the imbalance between the currents in the hot and neutral lines exceeds a predetermined value. The fault signal is typically monitored by fault sensing circuits which control the operation of a relay which is coupled to a bi-stable mechanical switch or circuit breaker located in the hot and/or neutral lines. When the magnitude of the fault signal generated by the differential transformers exceeds a predetermined value, the fault sensing circuit applies power to the relay, thereby causing the bi-stable mechanical circuit breaker to open.
In a typical prior art device, a pair of bi-stable switches are coupled in the hot and neutral lines, respectively. The individual utilizing the ground fault interruptor circuit manually places the switches in the closed position, so as to apply power from the power source to the load.
When the differential transformer detects an imbalance in the current flowing through the hot and neutral lines (indicative of a ground fault or other circuit fault), the ground fault interruptor circuit energizes a relay which opens the switches in the lines. Since the switches are bi-stable mechanical switches, they remain in the open position until they are manually reset.
A primary drawback of these prior art ground fault interruptor circuits is that they use mechanical bi-stable switches which are relatively large, expensive and, due to their mechanical nature, somewhat unreliable.
It has recently become common to utilize ground fault interruptor circuits in connection with household appliances, such as wet/dry vacuums While the present invention is not limited to such uses, it exhibits particular advantages in connection with such uses.
When using a ground fault interruptor with a household appliance, it is preferable to house the ground fault interruptor in the plug holding the male prongs which fit into a standard female wall receptacle In such cases, it is important that the ground fault interruptor circuit be small, inexpensive, and highly reliable.